Remove the dead cloudant_fake module

[MoonPointer-Byte]

Summary

• Delete the unused cloudant_fake.py stub module from the Cloudant provider
• Remove its entry from the OVERLOOKED_TESTS allowlist in test_project_structure.py

The module was a mypy fallback for Python 3.9 when ibmcloudant was excluded. Python 3.9 support was dropped in #52072 and the hook now imports CloudantV1 and CouchDbSessionAuthenticator directly from ibmcloudant. No remaining code references cloudant_fake.

Fixes #72269

Test plan

• Verified no remaining references to cloudant_fake in the repository
• breeze testing providers-tests providers/cloudant/tests/unit/cloudant
• breeze run mypy providers/cloudant/src/airflow/providers/cloudant

[boring-cyborg]

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[shahar1]

Thanks for your contribution!
As #72457 preceeded this PR and solves this issue the exact same way - I'll merge the former.
Feel free to solve other open issues.